1. Field of the Invention
The present invention relates in general to the field of lighting and signal processing, and more specifically to a system and method of time division light output sensing and adjustment for different spectra light emitting diodes.
2. Description of the Related Art
Light emitting diodes (LEDs) are becoming particularly attractive as main stream light sources in part because of energy savings through high efficiency light output and environmental incentives, such as the reduction of mercury. LEDs are a type of semiconductor devices and are driven by direct current. The brightness (i.e. luminous intensity) of the LED approximately varies in direct proportion to the current flowing through the LED. Thus, increasing current supplied to an LED increases the intensity of the LED and decreasing current supplied to the LED dims the LED. Current can be modified by either directly reducing the direct current level to the LEDs or by reducing the average current through duty cycle modulation.
FIG. 1 depicts lighting system 100, which includes lamp 102. Lamp 102 includes a light source 104 to generate artificial light 106. Light 106 reflects off the interior surface of the housing of lamp 102 and propagates through diffuser 108 to generate light 110. Lighting system 100 also includes an ambient light sensor 112 to facilitate light harvesting. Light harvesting involves supplementing artificial light 110 with natural light 114 and correlating adjustments in the artificial light with variations in the natural light. The physical location of ambient light sensor 112 is a matter of design choice. In at least one embodiment, ambient light sensor 112 is physically attached to the exterior of lamp 102. Location of ambient light sensor 112 on the exterior of the housing of lamp 102 assists in minimizing the contribution of artificial light 106 to the natural light 114 received by ambient light sensor 112. In at least one embodiment, ambient light sensor 112 is remotely located and communicates with controller 124 using any available communication technology.
Lamp 102 receives an alternating current (AC) voltage VAC—SUPPLY from supply voltage source 116 terminals 118 and 120. The voltage source 116 is, for example, a public utility, and the AC supply voltage VAC—SUPPLY is, for example, a 60 Hz/110 V line voltage in the United States of America or a 50 Hz/220 V line voltage in Europe.
Lighting system 100 includes a power control system 122 that includes controller 124 to control power provided to light source 104 and, thus, control the brightness of artificial light 110 generated by light source 104. Controller 124 generates control signal CS0 and provides control signal CS0 to lamp driver 126 to control power delivered by lamp driver 126 to light source 104. The particular configuration of lamp driver 126 is a matter of design choice and, in part, depends upon the configuration of light source 104. Light source 104 can be any type of light source, such as an incandescent, fluorescent, or LED based source. Lamp driver 126 provides power to light source 104 in accordance with control signal CS0.
Ambient light sensor 112 generates sense signal SEN1. Sense signal SEN1 indicates the brightness of ambient light. Controller 124 causes lamp driver 126 to increase or decrease the brightness of artificial light 110 if the ambient light is respectively too low or too high.
Light harvesting by lighting system 100 does not accurately account for the brightness of light 110 because the ambient light sensed by ambient light sensor 112 includes a contribution by artificial light 110.